initialization

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Param Patel

2024年04月30日 13:40

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Hello, 

How can I assign a constant value to a variable at a particular timestep?

i have a set {8,16,24,32}. I tried formulating it as a linear expression, (8b1+16b2+..), enforcing sum value as 1, thereby it can select any one value out of the set and append it to the variable r[i,j] at time-step j. 

If I take model.addVar(8,64,GRB.INTEGER) ---> This also does not work.

Later I want to retrieve the values of the variable and plot them.

Thank you.

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• 正式なコメント

  

  Simranjit Kaur

  • Gurobi Staff

  2026年11月13日 01:25

  This post is more than two years old. Some information may not be up to date. For current information, please check the Gurobi Documentation or Knowledge Base. If you need more help, please create a new post in the community forum, or try Gurobot, our chatbot interface offering instant, expert-level support.
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  Bot Marley (with AI contributions)

  2024年05月03日 00:42

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  Hi Param,

  To model a scenario where a variable can take only one value from a specified set at a particular time-step, and later use this variable for plotting or other purposes, you can utilize the capabilities of the Gurobi Optimizer in a more targeted manner. Here's a step-by-step explanation and a Python code snippet using the Gurobi Python API to achieve this:

  ### Defining the Problem
  You have a set \( \{8, 16, 24, 32\} \), and you want to assign exactly one of these values to a variable \( r[i, j] \) at time-step \( j \). This seems like a classic use-case for binary variables to select the value from the set.

  ### Step-by-Step Implementation
  1. **Variable Definitions**:
     - Define a binary variable for each value in the set for each timestep. For instance, \( b_8, b_{16}, b_{24}, b_{32} \) could be binary variables where \( b_k = 1 \) if \( r[i,j] = k \) and \( 0 \) otherwise.
     - Define \( r[i, j] \) as an integer or continuous variable depending on your specific requirements (e.g., sum of the products of set elements and corresponding binary variables).

  2. **Constraints**:
     - Ensure only one binary variable can take the value 1 at any time-step. This enforces that \( r[i, j] \) can only take one value from the set.
     - The value of \( r[i, j] \) should be equal to the sum of the products of each element in the set and its corresponding binary variable.

  3. **Objective (if any)**:
     - Depending on the broader problem, define an objective function.

  4. **Retrieving and Plotting Data**:
     - After solving the model, retrieve the value of \( r[i, j] \) for each timestep and use it for plotting or further analysis.

  This approach should solve your issue by setting up a decision variable linked with a set of binary variables to enforce the exclusive choice of values from your set.

   

  - Bot

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  Param Patel

  2024年05月06日 10:21 編集済み

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  Thank you for your reply. I tried that approach but it did not work 

  def model_variables_and_constraints(model, tk, v1_t, v2_t, e1, e2, v, T_full_charge, T_top_up, delta_t):

      r1t = {}

      e1t = {}

      # current_set = [8, 16, 24, 32, 48, 64]

  
  

      b1 = model.addVar(vtype=gb.GRB.BINARY, name='binary_var_current_8a')

      b2 = model.addVar(vtype=gb.GRB.BINARY, name='binary_var_current_16a')

      b3 = model.addVar(vtype=gb.GRB.BINARY, name='binary_var_current_24a')

      b4 = model.addVar(vtype=gb.GRB.BINARY, name='binary_var_current_32a')

      b5 = model.addVar(vtype=gb.GRB.BINARY, name='binary_var_current_48a')

      b6 = model.addVar(vtype=gb.GRB.BINARY, name='binary_var_current_64a')

  
  

      model.addConstr(gb.quicksum([b1,b2,b3,b4,b5,b6])==1)

      # Add the charging variables r and e for full charge and top-up EV

      for i in range(len(v1_t)):

          for j in range(len(tk)):

              r1t[i, j] = model.addVar(lb=0, ub=64, vtype=gb.GRB.INTEGER, name=f'EV_{i}_current_{j}')

              model.addConstr(r1t[i,j] == gb.quicksum([8*b1,16*b2,24*b3,32*b4,48*b5,64*b6]))

              e1t[i, j] = model.addVar(lb=0, ub=e1[i], vtype=gb.GRB.INTEGER, name=f'ChargingVariable_e1_{i}_{j}')

              if tk[i] <= tk[j] <= T_full_charge[i]:

                  model.addConstr(r1t[i, j] == 0)

  
  

      # Define constraints

      for i in range(len(v1_t)):

          for j in range(len(tk)):

              res = model.addVar(lb=0, ub=50000, vtype=gb.GRB.INTEGER, name=f'volts*current_{i}_{j}')

              final_res = model.addVar(lb=0, ub=50, vtype=gb.GRB.INTEGER, name=f'round_result_{i}_{j}')

              model.addConstr(res == r1t[i, j] * v * delta_t)

              model.addConstr(final_res == res / 1000)

              # Constraint to update pending energy based on cumulative charging completed till that step

              if tk[i]<=tk[j]<=T_full_charge[i]:

                  if j > 0:

                      model.addConstr(e1t[i, j] == e1[j-1] - final_res)

                  else:

                      model.addConstr(e1t[i, j] == e1[i] - final_res)

              else:

                  model.addConstr(e1t[i,j]==0)

   

  
  

      return r1t, e1t

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  Riley Clement

  • Gurobi Staff

  2024年05月06日 13:53

  Hi Param,

  How can I assign a constant value to a variable at a particular timestep?

  What is meant here by timestep?

  - Riley

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